Rotary drill bit including at least one superabrasive cutting element having a diamond-silicon carbide composite table

ABSTRACT

Embodiments relate to rotary drill bits that employ superabrasive cutting elements including a diamond-silicon carbide composite table. In an embodiment, a rotary drill bit includes a bit body configured to engage a subterranean formation. The bit body includes a plurality of blades. The rotary drill bit further includes a plurality of superabrasive cutting elements. Each of the superabrasive cutting elements is attached to a corresponding one of the cutting blades. At least one of the superabrasive cutting elements includes a substrate and a superabrasive table bonded to the substrate. The superabrasive table comprises diamond-silicon carbide composite including a matrix comprising nanometer-sized silicon carbide grains and micrometer-sized diamond grains dispersed through the matrix.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Application No. 13/173,292filed on 30 Jun. 2011, which is a divisional of U.S. application Ser.No. 12/001,990 filed on 12 Dec. 2007, which claims the benefit of U.S.Provisional Application No. 60/876,702 filed on 21 Dec. 2006 and U.S.Provisional Application No. 60/928,228 filed on 8 May 2007, thedisclosures of each of the foregoing applications are incorporatedherein, in their entirety, by this reference.

BACKGROUND

Wear-resistant, superabrasive compacts are utilized in a variety ofmechanical applications. For example, polycrystalline diamond (“PCD”)superabrasive compacts are used in drilling tools (e.g., cuttingelements, gage trimmers, etc.), machining equipment, bearingapparatuses, wire-drawing machinery, and in other mechanical systems.

Conventional polycrystalline diamond compacts (“PDCs”) have foundparticular utility as superabrasive cutting elements in rotary drillbits, such as roller cone drill bits and fixed cutter drill bits. Aconventional PDC cutting element or cutter typically includes asuperabrasive diamond layer or table. The diamond table is formed andbonded to a substrate using an ultra-high pressure, ultra-hightemperature (“HPHT”) process. The PDC cutting element may be brazeddirectly into a preformed pocket, socket, or other receptacle formed inthe rotary drill bit. In another configuration, the substrate may bebrazed or otherwise joined to an attachment member such as a stud or acylindrical backing. Such a stud carrying the PDC may be used as a PDCcutting element when mounted to a rotary drill bit by press-fitting,brazing, or otherwise securing the stud into a receptacle formed in therotary drill bit. Generally, a rotary drill bit may include one or morePDCs affixed to a bit body of the rotary drill bit.

Conventional PDCs are normally fabricated by placing a cemented carbidesubstrate into a container or cartridge with a volume of diamondparticles positioned on a surface of the cemented carbide substrate. Anumber of such cartridges may be typically loaded into an HPHT press.The substrates and volume of diamond particles are then processed underHPHT conditions in the presence of a catalyst material that causes thediamond particles to bond to one another to form a matrix of bondeddiamond grains defining a diamond table. The catalyst material is oftena solvent catalyst, such as cobalt, nickel, or iron that is used forfacilitating intergrowth between the diamond particles.

In one conventional approach, a constituent of the cemented carbidesubstrate, such as cobalt from a cobalt-cemented tungsten carbidesubstrate, liquefies and sweeps from the region adjacent to the volumeof diamond particles into interstitial regions between the diamondparticles during the HPHT process. The cobalt acts as a catalyst tofacilitate intergrowth between the diamond particles, which results inbonds between adjacent diamond particles. A solvent catalyst may bemixed with the diamond particles prior to subjecting the diamond grainsand substrate to the HPHT process.

The solvent catalyst dissolves carbon from the diamond particles orportions of the diamond particles that graphitize due to the hightemperature being used in the HPHT process. The solubility of the stablediamond phase in the solvent catalyst is lower than that of themetastable graphite under HPHT conditions. As a result of thissolubility difference, the undersaturated graphite tends to dissolveinto the solvent catalyst and the supersaturated diamond tends todeposit onto existing diamond particles to form diamond-to-diamondbonds. Accordingly, diamond particles become mutually bonded to form amatrix of PCD with interstitial regions between bonded diamond grainsbeing occupied by the solvent catalyst.

The presence of the solvent catalyst in the diamond table is believed toreduce the thermal stability of the diamond table at elevatedtemperatures. For example, the difference in thermal expansioncoefficient between the diamond grains and the solvent catalyst isbelieved to lead to chipping or cracking in the PDC during drilling orcutting operations, which consequently can degrade the mechanicalproperties of the PDC or cause failure. Additionally, some of thediamond grains can undergo a chemical breakdown or back-conversion tographite via interaction with the solvent catalyst. At extremely hightemperatures, portions of diamond grains may transform to carbonmonoxide, carbon dioxide, graphite, or combinations thereof, thus,degrading the mechanical properties of the PDC.

One conventional approach for improving the thermal stability of PDCs isto at least partially remove the solvent catalyst from the PDC by acidleaching. However, removing the solvent catalyst from the PDC can berelatively time consuming for high-volume manufacturing. Therefore,manufacturers and users of superabrasive materials continue to seekimproved thermally-stable superabrasive materials and processingtechniques.

SUMMARY

Embodiments of the present invention relate to diamond-silicon carbidecomposites, superabrasive compacts including such diamond-siliconcarbide composites, and methods of fabricating such diamond-siliconcarbide composites and superabrasive compacts. In one embodiment of thepresent invention, a superabrasive compact includes a substrate and asuperabrasive table bonded to the substrate. The superabrasive tablecomprises diamond-silicon carbide composite including a matrixcomprising nanometer-sized silicon carbide grains and micrometer-sizeddiamond grains dispersed through the matrix.

In some embodiments of the present invention, one or more transitionlayers may be disposed between the substrate and superabrasive table toreduce a residual stress gradient between the substrate andsuperabrasive table. In other embodiments of the present invention, atleast one layer of polycrystalline diamond may be disposed between thesuperabrasive table and substrate. In certain embodiments of the presentinvention, the superabrasive compact may include a barrier layerdisposed between the substrate and superabrasive table or disposedbetween another layer (e.g., as a transition layer or an intermediatePCD layer) and the superabrasive table.

In another embodiment of the present invention, a method of fabricatinga superabrasive compact is disclosed. An assembly comprising a mixtureincluding diamond particles and silicon is formed. The silicon maycomprise amorphous silicon, crystalline silicon crystallized fromamorphous silicon formed by a milling process, or combinations thereof.A substrate is positioned in proximity to the mixture. The assembly issubjected to heat and pressure to form a superabrasive compactcomprising a superabrasive table bonded to the substrate. Thesuperabrasive table comprises diamond-silicon carbide compositeincluding diamond grains dispersed through a matrix of silicon carbidegrains. In one embodiment of the present invention, one or moretransition layer mixtures may be positioned between the mixture andsubstrate to moderate residual stresses during formation of thesuperabrasive compact. In other embodiments of the present invention, atleast one layer of diamond particles may be disposed between the mixtureand substrate. In yet another embodiment of the present invention, abarrier layer may be disposed between the mixture and substrate to helpprevent silicon from the mixture from interacting with metal-solventcatalyst from the substrate or another source.

In another embodiment of the present invention for fabricating asuperabrasive compact, a superabrasive table comprising diamond-siliconcarbide composite may be separately formed and bonded to a substrate ora substrate carrying a transition layer. In yet another embodiment ofthe present invention, the superabrasive table comprisingdiamond-silicon carbide may be integrally formed with a transitionlayer, and the transition layer subsequently bonded to a substrate.

Additional embodiments of the present invention relate to applicationsutilizing the disclosed diamond-silicon carbide composites andsuperabrasive compacts in various articles and apparatuses, such asrotary drill bits, machining equipment, bearing apparatuses,wire-drawing dies, medical implements, and other articles andapparatuses.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate several embodiments of the present invention,wherein like reference numerals refer to like elements in differentviews or embodiments shown in the drawings.

FIG. 1 is a schematic diagram illustrating a method for fabricating asuperabrasive compact including a superabrasive table comprisingdiamond-silicon carbide composite according to various embodiment of thepresent invention.

FIG. 2 is a schematic diagram illustrating a method for fabricating asuperabrasive compact including a superabrasive table comprisingdiamond-silicon carbide composite, with an intermediate PCD layerpositioned between the superabrasive table and a substrate, according toone embodiment of the present invention.

FIG. 3 is a schematic side cross-sectional view of an assembly forforming a superabrasive compact including an intermediate-transitionlayer disposed between a superabrasive table comprising diamond-siliconcarbide composite and a substrate according to another embodiment of thepresent invention.

FIG. 4 is a schematic side cross-sectional view of the superabrasivecompact formed by HPHT sintering the assembly shown in FIG. 3.

FIG. 5 is a schematic side cross-sectional view of an assembly forforming a superabrasive compact including at least twointermediate-transition layers disposed between a superabrasive tablecomprising diamond-silicon carbide composite and a substrate accordingto another embodiment of the present invention.

FIG. 6 is a schematic side cross-sectional view of the superabrasivecompact formed by HPHT sintering the assembly shown in FIG. 5.

FIG. 7 is a schematic side cross-sectional view of a superabrasivecompact including barrier layer positioned between a superabrasive tablecomprising diamond-silicon carbide composite and a substrate accordingto one embodiment of the present invention.

FIG. 8 is a schematic side cross-sectional view of an assembly forforming the superabrasive compact shown in FIG. 7.

FIG. 9 is a schematic side cross-sectional view of a superabrasivecompact including non-planar barrier layer positioned between asuperabrasive table comprising diamond-silicon carbide composite and asubstrate according to one embodiment of the present invention.

FIG. 10 is a schematic side cross-sectional view of a superabrasivecompact including a barrier layer positioned between a superabrasivetable comprising diamond-silicon carbide composite and an intermediatePCD table according to another embodiment of the present invention.

FIG. 11 is a schematic side cross-sectional view of an assembly forforming the superabrasive compact shown in FIG. 10.

FIG. 12 is a schematic side cross-sectional view of a superabrasivecompact including a contoured barrier layer positioned between asuperabrasive table comprising diamond-silicon carbide composite and anintermediate PCD table according to another embodiment of the presentinvention.

FIG. 13 is a schematic side cross-sectional view of a superabrasivecompact including a non-planar barrier layer positioned between asuperabrasive table comprising diamond-silicon carbide composite and anintermediate PCD table according to yet another embodiment of thepresent invention.

FIG. 14 is a schematic side cross-sectional view of a superabrasivecompact including a contoured barrier layer positioned between anannular superabrasive region comprising diamond-silicon carbidecomposite and an intermediate PCD table according to a furtherembodiment of the present invention.

FIG. 15 is a schematic side cross-sectional view of a superabrasivecompact including a contoured barrier layer positioned between asuperabrasive table comprising diamond-silicon carbide composite and anintermediate PCD table according to yet further embodiment of thepresent invention.

FIG. 16A is an isometric view of one embodiment of a rotary drill bitincluding at least one superabrasive cutting element including asuperabrasive compact configured according any of the varioussuperabrasive compact embodiments of the present invention.

FIG. 16B is a top elevation view of the rotary drill bit of FIG. 16A.

FIG. 17A is an isometric partial cross-sectional view of athrust-bearing apparatus according to one embodiment of the presentinvention, which may utilize any of the disclosed superabrasive compactembodiments as bearing elements.

FIG. 17B is an isometric partial cross-sectional view of a radialbearing apparatus according to one embodiment of the present invention,which may utilize any of the disclosed superabrasive compact embodimentsas bearing elements.

FIG. 17C is a schematic isometric partial cross-sectional view of asubterranean drilling system including the thrust-bearing apparatusshown in FIG. 17A according to another embodiment of the presentinvention.

FIG. 18 is a graph illustrating wear characteristics as a function ofrock volume cut for various conventional PDCs and a cutting elementfabricated according to example 1 of the present invention.

FIG. 19 is a graph illustrating wear characteristics as a function ofrock volume cut for a conventional, fine grain, leached PDC and acutting element fabricated according to example 2 of the presentinvention and a superabrasive compact fabricated according to example 3of the present invention.

FIG. 20 is a graph illustrating wear characteristics as a function ofrock volume cut for a conventional, relatively, fine grain, leached PDCand a superabrasive compact fabricated according to example 4 of thepresent invention.

FIG. 21A is a low magnification photomicrograph taken using a scanningelectron microscope of a superabrasive compact fabricated according toexample 5 of the present invention.

FIG. 21B is a photomicrograph taken using a scanning electron microscopeshowing the microstructure of an upper region of the superabrasive tableshown in FIG. 21A.

FIG. 21C is a photomicrograph taken using a scanning electron microscopeshowing the microstructure of a lower region of the superabrasive tableshown in FIG. 21A.

FIG. 21D is a photomicrograph taken using a scanning electron microscopeshowing the microstructure of the superabrasive table shown in FIG. 21Aproximate the interface between the upper and lower regions.

FIG. 22 is graph of the silicon and cobalt concentrations in thesuperabrasive table shown in FIG. 21A.

FIG. 23 is a graph illustrating wear characteristics as a function ofrock volume cut for a conventional, relatively, fine grain, leached PDCand a superabrasive compact fabricated according to example 5 of thepresent invention.

FIG. 24A is a low magnification photomicrograph taken using a scanningelectron microscope of a superabrasive compact fabricated according toexample 6 of the present invention.

FIG. 24B is a photomicrograph taken using a scanning electron microscopeshowing the microstructure of an upper region of the superabrasive tableshown in FIG. 24A.

FIG. 24C is a photomicrograph taken using a scanning electron microscopeshowing the microstructure of a lower region of the superabrasive tableshown in FIG. 24A.

FIG. 24D is a photomicrograph taken using a scanning electron microscopeshowing the microstructure of the superabrasive table shown in FIG. 24Aproximate a transition region between the upper and lower regions.

FIG. 25 is graph of the silicon and cobalt concentrations in thesuperabrasive table shown in FIG. 24A.

FIG. 26 is a graph illustrating wear characteristics as a function ofrock volume cut for a conventional, relatively, fine grain, leached PDCand a superabrasive compact fabricated according to example 7 of thepresent invention.

FIG. 27 is a graph illustrating wear characteristics as a function ofrock volume cut for a conventional, relatively, fine grain, leached PDCand a superabrasive compact fabricated according to example 8 of thepresent invention.

DETAILED DESCRIPTION

Embodiments of the present invention relate to diamond-silicon carbidecomposites that comprise diamond grains dispersed in a matrix includingnanometer-sized silicon carbide grains. Methods of fabricating suchdiamond-silicon carbide composites and applications utilizing suchdiamond-silicon carbide composites are also disclosed. Thediamond-silicon carbide composites disclosed herein may be used in avariety of applications, such as drilling tools (e.g., superabrasivecompacts, gage trimmers, etc.), machining equipment, bearingapparatuses, wire-drawing machinery, and other apparatuses. As usedherein, the term “superabrasive” means a material that exhibits ahardness exceeding a hardness of tungsten carbide.

FIG. 1 schematically illustrates a method of fabricating a superabrasivecompact including a superabrasive table comprising diamond-siliconcarbide composite and the superabrasive compact so-formed according tovarious embodiments of the present invention. Referring to FIG. 1, aparticulate mixture 100 is positioned adjacent to an interfacial surface104 of a suitable substrate 102. The particulate mixture 100 maycomprise about 80 weight percent to about 90 weight percent diamondparticles and about 10 weight percent to about 20 weight percent siliconparticles. The diamond particles may exhibit an average particle size ofat least about 1 μm. More particularly, the diamond particles mayexhibit an average particle size of about 1 μm to about 150 μm, and morespecifically about 25 μm to about 40 μm. In some embodiments of thepresent invention, the diamond particles may exhibit a bi-modal orgreater distribution of nanometer-sized diamond particles with anaverage particle size of about 1 nm to about 150 nm and relativelylarger, micrometer-sized diamond particles with an average particle sizeof about 1 μm to about 100 μm. The nanometer-sized diamond particles mayinclude nanometer-sized conventional diamond particles, ultra-disperseddiamond particles as disclosed in U.S. patent application Ser. No.11/496,905, or both. U.S. patent application Ser. No. 11/496,905 isincorporated herein, in its entirety, by this reference. For example,the nanometer-sized diamond particles exhibiting an average particlesize of about 100 nm may comprise about 1 weight percent to about 6weight percent of the particulate mixture. In some embodiments of thepresent invention, the diamond particles may include agglomeratedgranules comprising diamond particles as disclosed in U.S. patentapplication Ser. No. 11/424,674, the disclosure of which is incorporatedherein, in its entirety, by this reference. The silicon particles mayexhibit an average particle size of about 1 μm to about 50 μm, and moreparticularly about 30 μm to about 40 μm.

In some embodiments of the present invention, the particulate mixture100 may be formed by mixing the diamond particles and silicon particlestogether using a ball mill (e.g., a planetary ball mill), an attritionmill, or the like. For example, milling apparatuses may employ one ormore mixing elements, such as balls, rods, or other shapes to effectmixing of the diamond and silicon particles. Optionally, such mixing maybe performed under an inert atmosphere, such as argon, for several hours(e.g., about 1 to about 30 hours). For example, the particulate mixture100 may be formed by ball milling the diamond particles and siliconparticles for three ball-mill cycles, each of which is about 95 minutesto about 100 minutes. In another embodiment of the present invention,the particulate mixture 100 may be formed by jet milling the diamondparticles and the silicon particles. In any of the above-mentionedmilling processes, the milling process may cause diamond particles tobecome at least partially or completely coated with a materialcomprising silicon. The parameters of the milling process may beselected and performed for a sufficient time to transform substantiallyall of the silicon particles from crystalline silicon to amorphoussilicon, with the milling time not being so long so that the diamondparticles and/or the silicon oxidize even when milled under asubstantially inert atmosphere. In other embodiments, the diamondparticles and silicon may be mixed with an organic liquid (e.g., heptaneor other organic liquid) to help prevent oxidation during the millingprocess, prevent agglomeration of the milled particles, or both.Additionally, the ball milling of the diamond particles and the siliconparticles may fracture a portion of the micrometer-sized diamondparticles to form nanometer-sized diamond particles (e.g., exhibiting asize of about 10 nm to about 100 nm). In another embodiment of thepresent invention, the silicon particles may be initially provided inamorphous form and mixed together with the diamond particles.

In other embodiments of the present invention, the diamond particles maybe coated with silicon using a deposition process, such as chemicalvapor deposition (“CVD”), physical vapor deposition (“PVD”), thermalspraying, or another suitable deposition process. The phrase“particulate mixture” used herein includes diamond particles at leastpartially coated with another material. Mixtures of diamond particlescoated by different methods may also be employed in any of theembodiments of the present invention disclosed herein.

In certain embodiments of the present invention, after intimately mixingthe diamond particles and the silicon particles, a tougheningconstituent may be mixed with the silicon-coated diamond particles. Forexample, in one embodiment of the present invention, the tougheningconstituent may comprise particles in the form of whiskers,polycrystalline particles, and/or single crystal particles comprised ofcarbides of Group IIA elements, IVA elements, IVB elements, VB elements,VIB elements, and combinations of any of the preceding carbides that maybe mixed with the silicon-coated diamond particles using any of theaforementioned mixing processes or a less aggressive mixing process,such as a Turbula® shaker-mixer from Willy A. Bachofen AGMaschinenfabrik of Basil, Switzerland. In a more specific embodiment ofthe present invention, the toughening constituent may comprise alphasilicon carbide particles, beta silicon carbide particles, or both. Inyet another embodiment of the present invention, the tougheningconstituent may comprise any other suitable silicon-based ceramic (e.g.,silicon nitride), aluminum-based ceramic (e.g., aluminum oxide),boron-based ceramic (e.g., boron oxides), iron/iron oxide-based ceramic,yttrium-based ceramic (e.g., yttrium oxide), zinc-based ceramic (e.g.,zinc oxide), zirconium-based ceramic (e.g., zirconium oxide), andcombinations of any of the preceding ceramics. The tougheningconstituent may comprise one or more of the aforementioned tougheningconstituents in an amount of about 1 to about 20 weight percent of theparticulate mixture 100. More specifically, the toughening constituentmay comprise about 1 to about 5 weight percent, about 5 to about 10weight percent, about 10 to about 15 weight percent, or about 15 toabout 20 weight percent of the particulate mixture.

Still referring to FIG. 1, the substrate 102 may be generallycylindrical or another selected configuration, without limitation.Although the interfacial surface 104 is illustrated as beingsubstantially planar, the interfacial surface 104 may exhibit a selectednonplanar topography, without limitation. The substrate 102 may includea metal-solvent catalyst, such as cobalt in a cobalt-cemented tungstencarbide or another suitable material. Other materials that may be usedfor the substrate 102 include, without limitation, cemented carbidesincluding titanium carbide, niobium carbide, tantalum carbide, vanadiumcarbide, and combinations of any of the preceding carbides cemented withcobalt, iron, nickel, or alloys thereof. The substrate 102 may alsocomprise a ceramic material that is not cemented with a metal-solventcatalyst.

The particulate mixture 100 and the substrate 102 are subjected to anHPHT sintering process to form a superabrasive compact 106 that includesa superabrasive table 108 bonded to the interfacial surface 104 of thesubstrate 102. The HPHT sintering process consolidates the particulatemixture 100 to form the superabrasive table 108 and bonds thesuperabrasive table 108 to the interfacial surface 104 of the substrate102. In order to sinter the particulate mixture 100 and the substrate102, the particulate mixture 100 and the substrate 102 may be placed ina pressure transmitting medium and/or other structure, such as arefractory metal can, graphite structure, pyrophyllite and/or otherpressure transmitting structure, or another suitable container orsupporting element. Methods and apparatuses for sealing enclosuressuitable for holding the particulate mixture 100 and the substrate 102are disclosed in U.S. patent application Ser. No. 11/545,929, which isincorporated herein, in its entirety, by this reference. In someembodiments of the present invention, the container for holding theparticulate mixture 100 and the substrate 102 is vacuum sealed at atemperature of about 1000° Celsius, which may partially or completelytransform amorphous silicon present in the particulate mixture tocrystalline silicon. When the particulate mixture 100 is formed bymilling the diamond particles and silicon in the presence of an organicliquid (e.g., heptane), the particulate mixture 100 may be dried beforeloading into the pressure transmitting medium.

The pressure transmitting medium, including the particulate mixture 100and the substrate 102, is subjected to an HPHT process using anultra-high pressure press at a temperature of at least about 1000°Celsius (e.g., about 1100° Celsius to about 2200° Celsius) and apressure of at least about 40 kilobar (e.g., about 50 kilobar to about80 kilobar) for a time sufficient to sinter the particulate mixture 100and form the superabrasive table 108 comprising the diamond-siliconcarbide composite. The HPHT sintering process also bonds thesuperabrasive table 108 to the substrate 102. During the HPHT sinteringprocess, the diamond particles and the silicon (e.g., silicon particlesor silicon coating the diamond particles) chemically react to formsilicon carbide. The silicon carbide formed from the reaction betweenthe diamond particles and the silicon may form beta silicon carbidehaving a face centered cubic (“FCC”) crystal structure. When alphasilicon carbide particles are present in the particulate mixture, thealpha silicon carbide particles may retain their hexagonal close packed(“HCP”) crystal structure even after the HPHT sintering process.

The resultant structure of the HPHT sintered diamond-silicon carbidecomposite comprising the superabrasive table 108 includesmicrometer-sized diamond grains dispersed in a matrix comprisingnanometer-sized silicon carbide grains. It is currently believed by theinventors that the presence of amorphous silicon in the particulatemixture 100 used to form the diamond-silicon carbide composite mayassist with nucleation of nanometer-sized silicon carbide grains insteadof micrometer-sized silicon carbide grains. The presence of amorphoussilicon in the particulate mixture 100 may assist with nucleation ofnanometer-sized silicon carbide grains even when the amorphous siliconis at least partially or completely transformed to crystalline siliconduring sealing of the container prior to subjecting the particulatemixture to HPHT sintering conditions. In some embodiments of the presentinvention, the matrix further includes nanometer-sized diamond grainsdispersed therethrough as a result of nanometer-sized diamond particlesused to form the particulate mixture 100, the milling process fracturingmicrometer-sized diamond particles into nanometer-sized diamondparticles, or both. The average grain size (i.e., post sintering) of thenanometer-sized silicon carbide grains and nanometer-sized diamondgrains in the matrix may be about 10 nm to about 900 nm, moreparticularly about 10 nm to about 500 nm, and even more particularlyabout 50 nm to about 200 nm (e.g., about 100 nm). The average grain sizeof the micrometer-sized diamond grains may be at least about 1 μm. Moreparticularly, the average grain size of the micrometer-sized diamondgrains may be about 1 μm to about 150 μm, and more specifically about 10μm to about 35 μm.

In certain embodiments of the present invention, the matrix may includeone or more of the aforementioned toughening constituents. For example,when alpha silicon carbide particles are added to the particulatemixture 100, the matrix of the diamond-silicon carbide composite mayalso comprise alpha silicon carbide grains and beta silicon carbidegrains formed from a reaction between the diamond particles and thesilicon. The combination of the alpha silicon carbide grains and thebeta silicon carbide gains may form needle-shaped alpha silicon carbidegrains at least partially surrounded by the beta silicon carbide grains,with the diamond grains dispersed through the matrix of alpha and betasilicon carbide. Such a microstructure for the matrix may impartimproved fracture toughness to the diamond-silicon carbide composite ofthe superabrasive table 108 compared to when only beta silicon carbideis present in the matrix.

The diamond-silicon carbide composite of the superabrasive table 108 mayexhibit superior mechanical properties that enable the superabrasivecompact 106 to be used in cutting and bearing applications. According tovarious embodiments of the present invention, the diamond-siliconcarbide composite of the superabrasive table 108 so-formed may exhibit afracture toughness of at least about 10 MPa·m^(1/2) to at least about 12MPa·m^(1/2), a Vickers hardness of at least about 35 GPa to at leastabout 50 GPa, and a Knoop hardness of at least about 25 GPa to at leastabout 45 GPa. The diamond-silicon carbide composites comprising thesuperabrasive table 108 may further exhibit a density of at least 95percent of theoretical density and, in some embodiments, fully dense(i.e., about 99 to about 100 percent of theoretical density).Additionally, because the HPHT diamond-silicon carbide compositecomprising the superabrasive table 108 may not be formed by liquidinfiltration of silicon into a mass of diamond powder, thediamond-silicon carbide composite so-formed may exhibit a substantiallyuniform density.

In one embodiment of the present invention, a two-step heating processmay be used to form the superabrasive compact 106. In such anembodiment, the particulate mixture 100 and substrate 102 are heated toa first temperature (e.g., at least about 800° Celsius) to partially orcompletely melt the silicon and held at the first temperature for a timesufficient to form the nanometer-sized silicon carbide grains of thediamond-silicon carbide composite of the superabrasive table 108. Then,the particulate mixture 100 and the substrate 102 are heated to a secondtemperature that is greater than the first temperature to melt themetal-solvent catalyst in the substrate 102 or from another source tobond the substrate 102 to the superabrasive table 108 so-formed. Inanother embodiment of the present invention, a one-step process may beused to form the superabrasive compact 106 by heating the particulatemixture 100 and the substrate 102 to at least the melting temperature ofthe metal-solvent catalyst. In one embodiment of the present invention,such a temperature is between about 900° Celsius to about 1500° Celsius.

In either the one-step or two-step heating processes, the metal-solventcatalyst may infiltrate a region of the particulate mixture 100 adjacentto the substrate 102 and at least two regions may be formed in thesuperabrasive table 108: (1) a lower region bonded to the substrate 102and (2) an upper region remote from the substrate 102. For example, whenthe substrate 102 comprises a cobalt-cemented tungsten carbidesubstrate, the lower region of superabrasive table 108 may includediamond grains dispersed in a matrix comprising one or more of thefollowing phases: cobalt, silicon carbide, cobalt silicide (e.g., Co₂Si,CoSi, and/or CoSi₂), and carbon precipitates. The upper region of thesuperabrasive table 108 remote from the substrate 102 may exhibit astructure as previously described above for the diamond-silicon carbidecomposite (i.e., diamond grains dispersed in a matrix includingnanometer-sized silicon carbide grains). Thus, the upper region may besubstantially free of metal-solvent catalyst, such as cobalt. Theformation of silicon carbide in the matrix of the upper region of thesuperabrasive table 108 may prevent further infiltration of the cobaltinto the upper region. The superabrasive table 108 may also include atransition region disposed between the lower and upper regions. Theconcentration of the cobalt in the transition region may more graduallydecrease with distance from the lower region compared to when a moredistinct boundary is present between the upper and lower regions.Despite the presence of metal-solvent catalyst in the lower region, thesuperabrasive table 108 may exhibit limited or substantially no directbonding between diamond grains. Thus, the superabrasive table 108 mayexhibit an absence of widespread and appreciable bonding between diamondgrains.

In other embodiments of the present invention, the superabrasive table108 may be separately formed using an HPHT sintering process and,subsequently, bonded to the interfacial surface 104 of the substrate 102by brazing, using a separate HPHT bonding process, or any other suitablejoining technique, without limitation. Again, when the substrate 102includes a metal-solvent catalyst, such as cobalt in a cobalt-cementedtungsten carbide substrate, metal-solvent catalyst may infiltrate aportion of the superabrasive table 108.

In yet another embodiment of the present invention, the superabrasivetable 108 may be separately formed using an HPHT sintering process and abinderless carbide layer, such as a tungsten carbide layer, may bedeposited on the superabrasive table 108 using CVD or physical vapordeposition (“PVD”), as disclosed in U.S. patent application Ser. No.11/899,691, to form a superabrasive compact and enable attaching thesuperabrasive compact to a bit body of a rotary drill bit. U.S. patentapplication Ser. No. 11/899,691 is incorporated herein, in its entirety,by this reference.

Referring to FIG. 2, in another embodiment of the present invention, asuperabrasive table may be formed by utilizing any of the previouslydescribed diamond-silicon formulations and a diamond particleformulation. A layer of diamond particles 110 is positioned adjacent tothe interfacial surface 104 of the substrate 102, and between thesubstrate 102 and particulate mixture 100. The particulate mixture 100,layer of diamond particles 110, and substrate 102 may be subjected to anHPHT sintering process to form a superabrasive compact 112. Thesuperabrasive compact 112 includes a superabrasive table 114 thatcomprises diamond-silicon carbide composite, as previously described,bonded to an intermediate PCD table 116, which is bonded to thesubstrate 102. During HPHT sintering, metal-solvent catalyst from thesubstrate 102 or another source may infiltrate the layer of diamondparticles 110 to form polycrystalline diamond with bonded diamond grainsand metal-solvent catalyst within the interstitial regions between thebonded diamond grains. A one-step or two-step heating process may alsobe used as previously described with respect to FIG. 1 to form thesuperabrasive compact 112. In one embodiment of the present invention,two or more layers of diamond particles may be disposed between theparticulate mixture 100 and the substrate 102. For example, each layerof diamond particles may be mixed with a different concentration ofmetal-solvent catalyst, with the layer adjacent to the substrate 102including a greater concentration of metal-solvent catalyst than a layeradjacent to the mixture 100.

Instead of HPHT sintering the layer of diamond particles 110, mixture100, and substrate 102 together, in another embodiment of the presentinvention, the particulate mixture 100 may be separately HPHT sinteredto form a free-standing superabrasive table 114. The separately formedsuperabrasive table 114 may be subsequently HPHT bonded or otherwisebonded to an upper surface of the PCD table 116 carried on the substrate102. In yet another embodiment of the present invention, the PCD table116 and the superabrasive table 114 may each be separately formed andthen bonded to the substrate 102 to form the superabrasive compact 112.In yet a further embodiment of the present invention, the superabrasivetable 114 and the PCD table 116 may be formed together in an HPHTprocess and then bonded to the substrate 102 in another HPHT process.

Although the precise physical phenomenon is not entirely understood, itis currently believed by the inventors that formation of nanometer-sizedsilicon carbide grains within the diamond-silicon carbide composite ofthe superabrasive table enhances bonding between the superabrasive tableand a substrate or an intermediate layer, such as a PCD layer or anintermediate transition layer.

Referring to FIGS. 3-6, additional embodiments of the present inventionrelate to superabrasive compacts including one or more transition layersformed between a superabrasive table and a substrate. The superabrasivetable may comprise any of the previously described diamond-siliconcarbide composites. Residual stresses in superabrasive compacts mayarise from a difference in thermal expansion between the superabrasivetable and the underlying substrate after sintering at HPHT. The residualstresses proximate to the interface between the substrate and thesuperabrasive table can be sufficient to fracture the bond between thesubstrate and the superabrasive table. Utilizing one or more transitionlayers can help moderate the residual stress developed duringmanufacture of the superabrasive compact so that the superabrasive tableremains securely attached to the substrate.

Referring to FIG. 3, an assembly 120 includes a substrate 102, a layerof the particulate mixture 100 comprising any of the previouslydescribed diamond-silicon formulations, and a transition layer mixture122 positioned between the substrate 102 and the particulate mixture100. The transition layer mixture 122 may be formulated to moderate theresidual stresses developed during HPHT sintering of the assembly 120and/or facilitate bonding between the particulate mixture 100 and thesubstrate 102. In one embodiment of the present invention, when thesubstrate 102 comprises a cemented tungsten carbide substrate, thetransition layer mixture 122 may comprise a mixture of tungsten-carbideparticles (or other metal-carbide particles) and diamond particles. In amore specific embodiment of the present invention, the tungsten-carbideparticles comprise about 20 volume percent to about 80 volume percentwith the diamond particles comprising the remaining volume percent ofthe transition layer mixture 122. A metal-solvent catalyst, such ascobalt, nickel, iron, or an Invar®-type iron-nickel alloy, may also beadded to the transition layer mixture 122.

FIG. 4 is a schematic side cross-sectional view of a superabrasivecompact 124 formed after HPHT sintering of the assembly 120. Thesuperabrasive compact 124 includes a superabrasive table 126 thatcomprises any of the previously described diamond-silicon carbidecomposites bonded to a transition layer 128 that comprisestungsten-carbide particles, cobalt (or other metal-solvent catalyst) anddiamond grains. The transition layer 128 is also bonded to the substrate102. During HPHT sintering, metal-solvent catalyst from the substrate102 (e.g., cobalt from a cobalt-cemented tungsten carbide substrate) oranother source sweeps into the transition layer mixture 122 to cementthe constituents of the transition layer mixture 122 together to formthe transition layer 128. Optionally, the transition layer 128 mayexhibit a thermal expansion coefficient greater than that of thesuperabrasive table 126, but less than that of the substrate 102 forreducing the residual stress gradient between the substrate 102 and thesuperabrasive table 126. Other formulations for the transition layermixture 122 and the resulting transition layer 128 may also be used toreduce the residual stress gradient between the substrate 102 and thesuperabrasive table 126 and/or improve bonding characteristics betweenadjacent regions of the differing materials.

In other embodiments of the present invention, more than one transitionlayer may comprise a superabrasive compact. Referring to the schematicside cross-sectional view of FIG. 5, an assembly 130 includes asubstrate 102, a layer of the particulate mixture 100 comprising any ofthe previously described diamond-silicon formulations, a firsttransition layer mixture 132 adjacent to the particulate mixture 100,and a second transition layer mixture 134 adjacent to the substrate 102.Optionally, the first transition layer mixture 132 may include lessmetal-carbide particles and more diamond particles than that of thesecond transition layer mixture 134 adjacent to the substrate 102. Inone embodiment of the present invention, when the substrate 102comprises a cemented tungsten carbide substrate, the first transitionlayer mixture 132 may comprise a mixture of tungsten-carbide particlesin an amount of about 30 volume percent and diamond particles in anamount of about 70 volume percent, and the second transition layermixture 134 may comprise a mixture of tungsten-carbide particles in anamount of about 70 volume percent and diamond particles in an amount ofabout 30 volume percent. A metal-solvent catalyst, such as cobalt,nickel, iron, or an Invar®-type iron-nickel alloy, may also be added tothe first and second transition layer mixtures 132 and 134.

Referring to the schematic side cross-sectional view of FIG. 6, afterHPHT sintering of the assembly 130, a superabrasive compact 136 isformed. The superabrasive compact 136 includes a superabrasive table 138that comprises any of the previously described diamond-silicon carbidecomposites bonded to a first transition layer 140 that comprisestungsten-carbide particles and diamond grains. A second transition layer142 is bonded to the first transition layer 140 and to the substrate102. During HPHT sintering, metal-solvent catalyst from the substrate102 (e.g., cobalt from a cobalt-cemented tungsten carbide substrate) oranother source sweeps into the first and second transition layermixtures 132 and 134 to cement the constituents thereof together.Optionally, if the first transition layer 140 includes relatively morediamond grains and less metal-carbide particles than that of the secondtransition layer 142, the residual stress gradient between the substrate102 and the superabrasive table 138 may be reduced. Other formulationsfor the transition layer mixtures 132, 134 and the resulting transitionlayers 140, 142 may be selected to reduce the residual stress gradientbetween the substrate 102 and the superabrasive table 138 and/orfacilitate bonding between regions comprising differing materials.

In another embodiment of the present invention, a superabrasive tablecomprising diamond-silicon carbide composite, as previously described,may be separately formed in an HPHT process and subsequently bonded to atransition layer formed on a substrate in a subsequent HPHT process. Inyet another embodiment of the present invention, a superabrasive tablecomprising diamond-silicon carbide composite, as previously described,bonded to one or more transition layers may be separately formed in anHPHT process and subsequently bonded to a substrate in a subsequent HPHTprocess. In yet a further embodiment of the present invention, asuperabrasive table comprising diamond-silicon carbide composite, aspreviously described, may be formed in a first HPHT process, a substratehaving one or more transition layer formed thereon may be formed in asecond HPHT process, and the superabrasive table may be bonded to one ofthe transition layers in a subsequent, third HPHT process.

In any of the above superabrasive compact embodiments of the presentinvention, a barrier layer may also be disposed between the particulatemixture 100 comprising a diamond-silicon formulation and a regionincluding a metal-solvent catalyst, such as the substrate 102 or atransition layer comprising polycrystalline diamond. A barrier layer mayhelp prevent chemical interaction between silicon in the particulatemixture 100 and metal-solvent catalyst (e.g., cobalt) during HPHTsintering. For example, FIG. 7 is a schematic side cross-sectional viewof a superabrasive compact 150 according to one embodiment of thepresent invention. The superabrasive compact 150 includes a barrierlayer 152 having a thickness, for example, of about 0.001 inch to about0.005 inch disposed between and bonded to a substrate 102 and asuperabrasive table 154 comprising any of the previously describeddiamond-silicon carbide composites. The barrier layer 152 may comprise arefractory material, such as tantalum, tungsten, niobium, molybdenum, oralloys of any of the preceding metals. The barrier layer 152 may alsocomprise materials, such as titanium, zirconium, alloys of any of thepreceding metals, or another suitable material. Additional materials forthe barrier layer 152 include, metal carbides, such as refractorymetal-carbides. For example, the barrier layer 152 may comprise tungstencarbide (e.g., binderless or low-binder tungsten carbide).

FIG. 8 is a schematic side cross-sectional view of an assembly 160,according to one embodiment of the present invention, which may be usedto form the superabrasive compact 150 shown in FIG. 7. The assembly 160includes a first container 162 that receives the substrate 102. A secondcontainer 164 is received by the first container 160, and receives theparticulate mixture 100. The second container 164 includes a barrierportion 165 that is positioned between the substrate 102 and aparticulate mixture 100 comprising any of the previously describeddiamond-silicon formulations. Accordingly, the second container 164 maybe formed from a refractory material, titanium, zirconium, alloys of anyof the preceding metals, or another suitable material. Ultimately, thebarrier portion 165 forms the barrier layer 152 shown in FIG. 7 afterHPHT sintering. A third container 166 receives the first container 162and a sidewall 167 thereof extends circumferentially about the firstcontainer 162. The first container 162 and the second container 164 maybe sealed together to substantially prevent silicon from the particlemixture 100 and metal-solvent catalyst (e.g., cobalt) from the substrate102 from interacting with each other during HPHT sintering. For example,a circumferentially extending bond 168 may be formed using laser weldingthat substantially seals the first container 162 and second container164 together. In another embodiment of the present invention, the bond168 may be formed by brazing the first container 162 and secondcontainer 164 together. The assembly 160 may further include acircumferentially extending bond 169 that substantially seals the firstcontainer 162 to the third container 166. As with the bond 168, the bond169 may be formed by laser welding or brazing.

In some embodiments of the present invention, the assembly 160 may beheated to a temperature of at least about 600° Celsius, and in somecases to a temperature of at least about 1100° Celsius in order tode-oxidize the diamond particles of the particulate mixture 100 andremove any surface-bonded hydrogen atoms from the diamond particlesprior to forming the bond 169. De-oxidizing the diamond particles andremoving any surface-bonded hydrogen atoms from the diamond particlesmay improve the bond between silicon carbide grains and diamond grainsin the final HPHT superabrasive compact. The aforementioned de-oxidizingprocess may be carried out under vacuum or a suitable inert or reducingenvironment. After sealing, and optionally cleaning the particulatemixture 100, the assembly 160 is subjected to HPHT process conditions tosinter the various components of the assembly 160 as previouslydescribed. After the HPHT process, an abrasive process, such as gritblasting, may be used to remove the first container 162 and the thirdcontainer 166. Except for the barrier portion 165, all of the secondcontainer 164 may also removed by an abrasive process to form thesuperabrasive compact 150 shown in FIG. 7. In another embodiment of thepresent invention, the second container 164 may be replaced with abarrier disc or other structure that is positioned between the substrate102 and the particulate mixture 100.

Still referring to FIG. 8, the barrier portion 165 of the secondcontainer 164 may be shaped to provide a non-planar barrier layer. Byshaping the barrier layer disposed between the substrate 102 and thesuperabrasive table comprising diamond-silicon carbide composite, thebond between the barrier layer and the substrate 102 may be enhanced dueto increased interfacial area and/or breaking-up internal stresses thatmay cause delamination during fabrication and use of a superabrasivecompact when the barrier layer is planar.

For example, a superabrasive compact 165, according to one embodiment ofthe present invention, is shown in the schematic side cross-sectionalview of FIG. 9. The superabrasive compact 165 includes a non-planerbarrier layer 166 bonded to a correspondingly shaped interfacial surface167 of the substrate 102. A superabrasive table 168 comprising any ofthe previously described diamond-silicon carbide composites is bonded tothe barrier layer 166. It should be emphasized that the non-planarbarrier layer 166 illustrated in FIG. 9 is merely one suitableconfiguration, and other barrier-layer configurations may be used toprovide a more delamination resistant barrier layer.

FIG. 10 is a schematic side cross-sectional view of a superabrasivecompact 170, according to another embodiment of the present inventionthat also utilizes a barrier layer to help prevent interaction betweensilicon and metal-solvent catalyst. The superabrasive compact 170includes a barrier layer 172 disposed between and bonded to anintermediate PCD table 174 and a superabrasive table 176 comprising anyof the previously described diamond-silicon carbide composites. Theintermediate PCD table 174 is bonded to the substrate 102. Theintermediate PCD table 174 comprises bonded diamond grains withinterstitial regions between the bonded diamond grains occupied withmetal-solvent catalyst (e.g., cobalt) swept-in from the substrate 102 orfrom another source. In one embodiment of the present invention, theintermediate PCD table 174 may comprise two or more PCD layers, with theconcentration of the metal-solvent catalyst within the PCD layeradjacent to the substrate 102 being greater than the concentration ofthe metal-solvent catalyst within the PCD layer adjacent to the barrierlayer 172.

FIG. 11 is a schematic side cross-sectional view of an assembly 180,according to one embodiment of the present invention, which may be usedto form the superabrasive compact 170 shown in FIG. 10. The assembly 180includes a first container 182 that receives a particulate mixture 100comprising any of the previously described diamond-silicon formulations.A second container 184 is received by the first container 182 and alsoholds a layer of diamond particles 181. Metal-solvent catalyst, such ascobalt, may be mixed with the layer of diamond particles 181. Thesubstrate 102 is also received by the second container 184 andpositioned adjacent to the layer of diamond particles 181. The secondcontainer 184 includes a barrier portion 185 positioned adjacent to theparticulate mixture 100 that helps prevent metal-solvent catalyst fromthe substrate 102 or, if present, the layer of diamond particles 181from interacting with silicon in the particulate mixture 100 during HPHTsintering. Accordingly, the second container 184 may be formed from thesame materials as the second container 164 shown in FIG. 8. Ultimately,the barrier portion 185 forms the barrier layer 172 shown in FIG. 10after HPHT sintering. A third container 186 receives the first container182 and a sidewall 187 thereof extends circumferentially about the firstcontainer 182. The first container 182 and the second container 184 maybe sealed together with a circumferentially extending bond 188 and thethird container 186 and the first container 182 may be sealed togetherwith a circumferentially extending bond 189, as previously describedwith respect to the assembly 160 shown in FIG. 8. After sealing, andoptionally cleaning the particulate mixture 100 using a high-temperatureprocess, the assembly 180 is subjected to HPHT process conditions tosinter various components of the assembly 180 as previously described.After the HPHT process, an abrasive process, such as grit blasting, maybe used to remove the first container 182 and the third container 186.Except for the barrier portion 185, all of the second container 184 isalso removed by an abrasive process to form the superabrasive compact170 shown in FIG. 10. Similar to the assembly 160 shown in FIG. 8, thesecond container 184 may be replaced with a barrier disc positionedbetween the particulate mixture 100 and the layer of diamond particles181.

The barrier portion 185 of the second container 184 shown in FIG. 11 maybe shaped to provide a selected contour to a barrier layer of an HPHTsintered superabrasive compact. By shaping the barrier layer between theintermediate PCD table and the superabrasive table comprisingdiamond-silicon carbide composite, the volume of the diamond-siliconcarbide composite may be reduced, which generally has a lower strengththan an underlying PCD table. Thus, the intermediate PCD table mayprovide a strong core, with a relatively less strong, morethermally-stable superabrasive layer formed over the intermediate PCDtable. For example, a superabrasive compact 190, according to oneembodiment of the present invention, is shown in FIG. 12. Thesuperabrasive compact 190 includes an intermediate PCD table 192 bondedto the substrate 102, a contoured barrier layer 194 bonded to the PCDtable 192, and a superabrasive table 196 comprising any of thepreviously described diamond-silicon carbide composites bonded to thebarrier layer 194. A cutting surface 197 of the superabrasive table 196may be defined after HPHT sintering using grinding, machining (e.g.,electro-discharge machining), or another suitable material removalprocess.

In addition to shaping the barrier portion 185 of the second container186 shown in FIG. 11 to provide a contoured barrier layer, the barrierportion 185 may be shaped so that an interface between the barrier layerand the PCD table and an interfacial surface between the barrier layerand a superabrasive table exhibits a selected non-planar topography. Anon-planar topography for the barrier layer may provide increasedsurface area to increase the bond strength between the barrier layer andthe PCD table and the superabrasive table. Moreover, a non-planarbarrier layer helps break-up internal stresses, thereby reducing thelikelihood of delamination of the barrier layer from the intermediatePCD table during fabrication of a superabrasive compact and use.

FIG. 13 is a schematic side cross-sectional view of a superabrasivecompact 200 according to one embodiment of the present invention thatutilizes a non-planar barrier layer 202. The non-planar barrier layer202 is bonded to an intermediate PCD table 204 and a superabrasive table206 comprising any of the previously described diamond-silicon carbidecomposites. The non-planar barrier layer 202 is merely one suitableconfiguration, and other barrier-layer configurations may be used toprovide a more delamination resistant barrier layer.

FIG. 14 is a schematic side cross-sectional view of a superabrasivecompact 210 according to yet another embodiment of the presentinvention. In the superabrasive compact 210, the superabrasive table maycomprise one or more superabrasive regions 212. The superabrasive region212 may comprise any of the previously described diamond-silicon carbidecomposites. For example, the superabrasive compact 210 is shown with anannular-shaped superabrasive region 212 that extends circumferentiallyabout an intermediate PCD table 214. A contoured barrier layer 216 isdisposed between and bonded to the superabrasive region 212 and the PCDtable 214. It should be noted that the PCD table 214 provides arelatively stronger, more fracture resistant core, while thesuperabrasive region 212 provides a more wear resistant andthermally-stable cutting region.

FIG. 15 is a schematic side cross-sectional view of a superabrasivecompact 220 according to an additional embodiment of the presentinvention. In the superabrasive compact 220, a barrier layer 222 isshaped to contour an intermediate PCD table 224 that is bonded to thesubstrate 102. A superabrasive table 226 comprising any of thepreviously described diamond-silicon carbide composites is bonded to thebarrier layer 222. In such an embodiment, the superabrasive table 226 isshaped to also contour the barrier layer 222 so that the superabrasivetable 226 exhibits substantially vertical side cutting surfaces 228.

In addition to the various embodiments of superabrasive compactsdescribed herein, slugs of the diamond-silicon carbide composite may befabricated and employed without being bonded to a substrate. Forexample, according to other embodiments of the present invention, slugsof the diamond-silicon carbide composite may be formed to an appropriateconfiguration for use as a machining cutting element or for use as acutting element that is press-fit into a recess of a drill bit body(e.g., a steel bit body) of a rotary drill bit. Other applications forslugs of the diamond-silicon carbide composite include casting the slugsinto a matrix-type drill bit body.

Further embodiments of the present invention herein relate to articlesof manufacture comprising a body including a layer comprising anydiamond-silicon carbide composite disclosed herein bonded to the bodyvia brazing, an HPHT process, or another suitable joining technique. Forexample, in one embodiment of the present invention, the body may beconfigured as a medical implement (e.g., a surgical tool like a scalpel)in which the layer comprising diamond-silicon carbide composite providesa wear-resistant, generally inert, and sharpened cutting edge or point.Other medical implements include boring tools and rasps.

FIG. 16A is an isometric view and FIG. 16B is a top elevation view of arotary drill bit 250 according to one embodiment of the presentinvention. The rotary drill bit 250 includes at least one superabrasivecutting element configured according to any of the previously describedsuperabrasive compact embodiments. The rotary drill bit 250 comprises abit body 252 that includes radially and longitudinally extending blades254 with leading faces 256, and a threaded pin connection 258 forconnecting the bit body 252 to a drilling string. The bit body 252defines a leading end structure for drilling into a subterraneanformation by rotation about a longitudinal axis 260 and application ofweight-on-bit.

Still referring to FIGS. 16A and 16B, at least one superabrasive cuttingelement, configured according to any of the previously describedsuperabrasive compact embodiments, may be affixed to rotary drill bit250. Referring to FIG. 16B, a plurality of cutting elements 262 aresecured to the blades 254. For example, each cutting element 262 mayinclude a superabrasive table 264 (e.g., comprising diamond-siliconcarbide composite) bonded to a substrate 266. More generally, thecutting elements 262 may be configured as any of the superabrasivecompact embodiments disclosed herein, without limitation. In someembodiments of the present invention, the cutting elements 262 may beformed by separately forming a superabrasive table comprising anydiamond-silicon carbide composite disclosed herein (i.e., without asubstrate) and affixing the superabrasive table to the bit body 252. Forexample, structures as previously discussed and disclosed in U.S. patentapplication Ser. No. 11/899,691 may be employed. In addition, ifdesired, in some embodiments of the present invention, a number of thecutting elements 262 may be conventional in construction. Also,circumferentially adjacent blades 254 define so-called junk slots 268therebetween, as known in the art. Additionally, the rotary drill bit250 includes a plurality of nozzle cavities 270 for communicatingdrilling fluid from the interior of the rotary drill bit 250 to thecutting elements 262.

FIGS. 16A and 16B merely depict one embodiment of a rotary drill bitthat employs at least one cutting element comprising diamond-siliconcarbide composite fabricated and structured in accordance with thedisclosed embodiments, without limitation. The rotary drill bit 250 maybe used to represent any number of earth-boring tools or drilling tools,including, for example, core bits, roller-cone bits, fixed-cutter bits,eccentric bits, bicenter bits, percussion bits, reamers, reamer wings,or any other downhole tool including superabrasive cutting elements orinserts, without limitation.

The diamond-silicon carbide composites and superabrasive compactsdisclosed herein may also be utilized in applications other than cuttingtechnology. For example, the disclosed diamond-silicon carbidecomposites and superabrasive compacts may be used in wire dies,bearings, artificial joints, heart valves, inserts, and heat sinks Anyof the diamond-silicon carbide composites and superabrasive compactsdisclosed herein may be employed in an article of manufacture includingat least one superabrasive element or compact. Thus, the embodiments ofdiamond-silicon carbide composites and superabrasive compacts disclosedherein may be used on any apparatus or structure in which at least oneconventional PCD element or compact is typically used. For example, inone embodiment of the present invention, a rotor and a stator (i.e., athrust bearing apparatus) may each include a superabrasive element orcompact comprising diamond-silicon carbide composite according to any ofthe embodiments disclosed herein and may be operably assembled to adownhole drilling assembly. U.S. Pat. Nos. 4,410,054; 4,560,014;5,364,192; 5,368,398; and 5,480,233, the disclosure of each of which isincorporated herein, in its entirety, by this reference, disclosesubterranean drilling systems within which bearing apparatuses utilizingdiamond-silicon carbide composites and superabrasive compacts disclosedherein may be incorporated.

The embodiments of diamond-silicon carbide composites and superabrasivecompacts disclosed herein may also form all or part of heat sinks, wiredies, bearing elements, cutting elements, cutting inserts (e.g., on aroller cone type drill bit), machining inserts, or any other article ofmanufacture as known in the art. Other examples of articles ofmanufacture that may use any of the diamond-silicon carbide compositesand superabrasive compacts disclosed herein are disclosed in U.S. Pat.Nos. 4,811,801; 4,274,900; 4,268,276; 4,468,138; 4,738,322; 4,913,247;5,016,718; 5,092,687; 5,120,327; 5,135,061; 5,154,245; 5,460,233;5,544,713; and 6,793,681, the disclosure of each of which isincorporated herein, in its entirety, by this reference.

FIG. 17A is an isometric partial cross-sectional view of athrust-bearing apparatus 272 according to one embodiment of the presentinvention, which may utilize any of the disclosed superabrasive compactembodiments as bearing elements. The thrust-bearing apparatus 272includes respective bearing assemblies 274. Each bearing assembly 274includes a support ring 276 that may be fabricated from a material, suchas steel, stainless steel, or another suitable material. Each supportring 276 includes a plurality of recesses (not labeled) that receives acorresponding bearing element 278. Each bearing element 278 may bemounted to a corresponding support ring 276 within a correspondingrecess by brazing, press-fitting, using fasteners, or another suitablemounting technique. One or more, or all of bearing elements 278 may beconfigured according to any of the disclosed superabrasive compactembodiments. For example, each bearing element 278 may include asubstrate 280 and a superabrasive table 282 comprising diamond-siliconcarbide composite, with the superabrasive table 282 including a bearingsurface 284.

In use, the bearing surfaces 284 of one of the bearing assemblies 274bears against the opposing bearing surfaces 284 of the other one of thebearing assemblies 274. For example, one of the bearing assemblies 274may be operably coupled to a shaft to rotate therewith and may be termeda “rotor.” The other one of the bearing assemblies 274 may be heldstationary and may be termed a “stator.”

FIG. 17B is an isometric view of a radial bearing apparatus 275according to another embodiment of the present invention, which mayutilize any of the disclosed superabrasive compact embodiments asbearing elements. The radial bearing apparatus 275 includes an innerrace 277 positioned generally within an outer race 279. The outer race279 includes a plurality of bearing elements 281 affixed thereto and aninner race 277 also includes a plurality of bearing elements 283 affixedthereto. One or more, or all of the bearing elements 281 and 283 may beconfigured according to any of the superabrasive compact embodimentsdisclosed herein. The inner race 277 is positioned generally within theouter race 279. Thus, inner race 277 and outer race 279 may beconfigured so that the bearing surfaces (collectively defined by therespective bearing elements 283 affixed to the inner race 277 and therespective bearing elements 281 affixed to the outer race 279) may atleast partially contact one another and move relative to each other asthe inner race 277 and outer race 279 rotate relative to each otherduring use.

Referring to FIG. 17C, the thrust-bearing apparatus 272 and/or radialbearing apparatus 275 may be incorporated in a subterranean drillingsystem. FIG. 17C is a schematic isometric partial cross-sectional viewof a subterranean drilling system 284 that includes the thrust-bearingapparatus 272 shown in FIG. 17A according to another embodiment of thepresent invention. The subterranean drilling system 284 includes ahousing 286 enclosing a downhole drilling motor 288 (i.e., a motor,turbine, or any other device capable of rotating an output shaft) thatis operably connected to an output shaft 290. The thrust-bearingapparatus 272 shown in FIG. 17A is operably coupled to the downholedrilling motor 288. A rotary drill bit 292 configured to engage asubterranean formation and drill a borehole is connected to the outputshaft 290. The rotary drill bit 292 is shown as a roller cone bitincluding a plurality of roller cones 294. However, other embodiments ofthe present invention may utilize different types of rotary drill bits,such as so-called “fixed cutter” drill bits. As the borehole is drilled,pipe sections may be connected to the subterranean drilling system 284to form a drill string capable of progressively drilling the borehole toa greater depth within the earth.

One of the thrust-bearing assemblies 274 of the thrust-bearing apparatus272 is configured as a stator that does not rotate and the other one ofthe thrust-bearing assemblies 274 is configured as a rotor that isattached to the output shaft 290 and rotates with the output shaft 290.

In operation, drilling fluid may be circulated through the downholedrilling motor 288 to generate torque and effect rotation of the outputshaft 290 and the rotary drill bit 292 attached thereto so that aborehole may be drilled. A portion of the drilling fluid may also beused to lubricate opposing bearing surfaces of the bearing elements 278of the thrust-bearing assemblies 274.

The following working examples of the present invention set forthvarious formulations for forming diamond-silicon carbide composites,cutting elements, and superabrasive compacts including a tablecomprising diamond-silicon carbide composite. The following workingexamples provide further detail in connection with the specificembodiments described above.

Example 1

A mixture comprising about 79 weight percent diamond particles with aparticle size of about 30 μm to about 40 μm, about 5 weight percentdiamond particles with an average particle size of about 0.1 μm (100nm), and about 16 weight percent crystalline silicon particles with anaverage particle size of about 35 μm was loaded into a tungsten carbidemilling jar and purged with argon gas. Then, the mixture was mixed in aSpex 8000D mixer/mill milling apparatus using tungsten carbide balls forabout 24 hours. X-ray diffraction analysis of the milled mixtureconfirmed that during the milling process, the silicon particlesgradually transformed from crystalline silicon to amorphous silicon dueto introduction of defects from the milling of the silicon particles inthe presence of diamond particles. Particle size analysis showed thatthe particle size of the diamond particles was reduced due to themilling process. The particle size of the diamond particles aftermilling ranged from about 40 nm to about 40 μm, and the milled diamondparticles were coated with a thin layer of amorphous silicon.

The milled mixture was placed in a boron nitride capsule, cleaned usinga high-temperature vacuum process, and vacuum sealed. The capsule,including the milled mixture, was placed in the reaction zone of aconventional high-temperature, high-pressure apparatus and subjected toa temperature of about 1400° Celsius and a pressure of about 60 kilobarfor about 6 minutes to sinter the milled mixture and form adiamond-silicon carbide composite. X-ray diffraction analysis showedthat the major phases present in the diamond-silicon carbide compositewere about 75 volume percent diamond and about 25 volume percent siliconcarbide.

The diamond-silicon carbide composite so-formed was machined into acylindrical cutting element with a diameter of about 13 mm and a lengthof about 13 mm for wear and thermal stability testing. The wearresistance of the diamond-silicon carbide composite of example 1 wascompared to several conventional PDC formed from different diamondparticle formulations exhibiting different average particle sizes (12μm, 20 μm, and 40 μm). The wear resistance was evaluated by measuringthe volume of the cutting element removed versus the volume of SierraWhite Granite rock removed in a vertical turret lathe at a 0.010 inchdepth of cut and 100 RPM, with water used as a coolant. As shown in FIG.18, the cutting element of example 1 exhibited significantly less wearwhen compared to the conventional PDCs.

The thermal stability of the diamond-silicon carbide composite ofexample 1 was evaluated by measuring the distance cut in a Sierra WhiteGranite workpiece in a vertical turret lathe at a 0.110 inch depth ofcut and 100 RPM, without using coolant. The cutting element of example 1was able to cut a distance approximately 7.8 times greater than aconventional, fine grain, PDC prior to thermal failure. The diamondtable of the conventional PDC used in the thermal stability tests wasleached to a depth of about 70 μm to remove nearly all of the cobaltfrom a region of the diamond table. Thus, the cutting element of example1 exhibited a significantly greater thermal stability than theconventional, fine grain, PDC.

Example 2

A mixture comprising about 79 weight percent diamond particles with aparticle size of about 30 μm to about 40 μm, about 5 weight percentdiamond particles with an average particle size of about 0.1 μm (100nm), and about 16 weight percent crystalline silicon particles with anaverage particle size of about 35 μm was loaded into a tungsten carbidemilling jar and purged with argon gas. Then, the mixture was mixed in aSpex 8000D mixing/milling apparatus using tungsten carbide balls forabout 8 hours. The milled mixture was placed in a niobium capsule,cleaned using a high-temperature vacuum process, and vacuum sealed. Thecapsule, including the milled mixture, was placed in the reaction zoneof a conventional high-temperature, high-pressure apparatus andsubjected to a temperature of about 1400° Celsius and a pressure ofabout 60 kilobar for about 6 minutes to sinter the milled mixture andform a diamond-silicon carbide composite. X-ray diffraction analysisshowed that the major phases present in the diamond-silicon carbidecomposite were diamond and silicon carbide. The diamond-silicon carbidecomposite so-formed was machined into a cylindrical cutting element witha diameter of about 13 mm and a length of about 8 mm for wear andthermal stability testing.

As shown in FIG. 19, the cutting element of example 2 exhibited wearresistance similar to a conventional, fine grain, PDC. The diamond tableof the conventional PDC used in the wear resistance test was leached toa depth of about 70 μm to remove nearly all of the cobalt from a regionof the diamond table. The thermal stability of the cutting element ofexample 2 was evaluated by measuring the distance cut in a Sierra WhiteGranite workpiece in a vertical turret lathe at a 0.110 inch depth ofcut and 100 RPM, with out using coolant. The cutting element of example2 was able to cut a distance approximately 23 times greater than that ofa conventional, fine grain, PDC similar to the conventional PDC used inthe wear resistance tests of example 1. Thus, the cutting element ofexample 2 exhibited a significantly greater thermal stability than theconventional, fine grain, PDC.

Example 3

A first layer comprising about 1 gram of the milled mixture of diamondparticles and silicon previously described in example 2 was distributedin the bottom of a niobium capsule. A second layer comprising about 1gram of diamond particles with a particle size range of about 15 μm toabout 25 μm was layered over the first layer. A cobalt-cemented tungstencarbide substrate was placed over the second layer of diamond particles.Then, the niobium capsule including the first layer, second layer, andsubstrate was cleaned using a high-temperature vacuum process and vacuumsealed. The niobium capsule, including the first layer, second layer,and substrate, was placed in the reaction zone of a conventionalhigh-temperature, high-pressure apparatus and subjected to a temperatureof about 1400° Celsius and a pressure of about 60 kilobar for about 6minutes to bond the various layers together and bond the second layer tothe substrate. The superabrasive compact so-formed included a table ofdiamond-silicon carbide composite defining a cutting region, acobalt-cemented tungsten carbide substrate, and an intermediatepolycrystalline diamond table sintered with cobalt swept in from thesubstrate that is bonded to the substrate and the table ofdiamond-silicon carbide composite.

The superabrasive compact so-formed was machined to a diameter of about16 mm and a length of about 8 mm for wear and thermal stability testing.The wear resistance of the superabrasive compact of example 3 was alsoevaluated by measuring the volume of the cutting element removed versusthe volume of Sierra White Granite rock removed in a vertical turretlathe at a 0.010 inch depth of cut and 100 RPM, with water used as acoolant. As shown in FIG. 19, the superabrasive compact of example 3exhibited wear resistance similar to the conventional, fine grain, PDCpreviously described in example 1. The thermal stability of thesuperabrasive compact of example 3 was also evaluated by measuring thedistance cut in a Sierra White Granite workpiece in a vertical turretlathe at a 0.110 inch depth of cut and 100 RPM, without using coolant.The superabrasive compact of example 3 was able to cut a distanceapproximately 7 times greater than that of a conventional, fine grain,PDC similar to the conventional PDC previously described in example 1.Thus, the superabrasive compact of example 3 exhibited a significantlygreater thermal stability than the conventional, fine grain, PDC.

Example 4

A mixture comprising about 83 weight percent diamond particles with aparticle size of about 30 μm to about 40 μm, about 3 weight percentdiamond particles with an average particle size of about 0.1 μm (100nm), and about 14 weight percent crystalline silicon particles with anaverage particle size of about 35 μm was loaded into a tungsten carbidemilling jar and purged with argon gas. The mixture was then mixed in aSpex 8000D mixing/milling apparatus using tungsten carbide balls forabout 1.67 hours.

A first layer comprising about 1 gram of the milled mixture wasdistributed in the bottom of a niobium capsule. A second layercomprising about 1 gram of diamond particles with a particle size ofabout 15 μm to about 25 μm was layered over the first layer. Acobalt-cemented tungsten carbide substrate was placed over the secondlayer of diamond particles. The niobium capsule including the firstlayer, second layer, and substrate was cleaned using a high-temperaturevacuum process and vacuum sealed. Then, the niobium capsule, includingthe first layer, second layer, and substrate, was placed in the reactionzone of a conventional high-temperature, high-pressure apparatus andsubjected to a temperature of about 1400° Celsius and a pressure ofabout 60 kilobar for about 6 minutes to bond the various layers togetherand bond the second layer to the substrate. The superabrasive compactso-formed included a table of diamond-silicon carbide composite defininga cutting region, a cobalt-cemented tungsten carbide substrate, and anintermediate polycrystalline diamond table sintered with cobalt swept infrom the substrate that is bonded to the substrate and the table ofdiamond-silicon carbide composite.

The superabrasive compact so-formed was machined to a diameter of about16 mm and a length of about 13 mm for wear and thermal stabilitytesting. The wear resistance of the superabrasive compact of example 4was also evaluated by measuring the volume of the cutting elementremoved versus the volume of Sierra White Granite rock removed in avertical turret lathe at a 0.010 inch depth of cut and 100 RPM, withwater used as a coolant. As shown in FIG. 20, the superabrasive compactof example 4 exhibited wear resistance similar to the conventional, finegrain, PDC described above in example 1. The thermal stability of thesuperabrasive compact of example 4 was also evaluated by measuring thedistance cut in a Sierra White Granite workpiece in a vertical turretlathe at a 0.110 inch depth of cut and 100 RPM, without using coolant.The superabrasive compact of example 4 was able to cut a distanceapproximately 12 times greater than that of a conventional, fine grain,PDC similar to the conventional PDC described above in example 1. Thus,the superabrasive compact of example 4 exhibited a significantly greaterthermal stability than the conventional, fine grain, PDC.

Drop-weight tests also indicated that the table of diamond-siliconcarbide composite of the superabrasive compact of example 4 exhibited animpact resistance similar to the conventional, fine grain, PDC used inthe wear resistance and thermal stability tests of example 2-4.

Example 5

A mixture comprising about 85 weight percent diamond particles with aparticle size of about 15 μm to about 25 μm, about 5 weight percentdiamond particles with an average particle size of about 1 μm to about 3μm, and about 10 weight percent crystalline silicon particles with anaverage particle size of about 35 μm was loaded into a tungsten carbidelined milling jar and purged with argon gas. The mixture was then mixedin a Spex 8000D mixing/milling apparatus using tungsten carbide ballsfor about 1.67 hours.

A layer comprising about 2 grams of the milled mixture was distributedin the bottom of a niobium capsule. A cobalt-cemented tungsten carbidesubstrate was placed over the layer of the milled mixture, with a planarinterfacial surface of the substrate positioned adjacent to the layer.The niobium capsule, including the layer of the milled mixture andsubstrate, was cleaned using a high-temperature vacuum process andvacuum sealed. Then, the niobium capsule, including the layer of themilled mixture and substrate, was placed in the reaction zone of aconventional high-temperature, high-pressure apparatus and subjected toa temperature of about 1400° Celsius and a pressure of about 60 kilobarfor about 6 minutes.

The superabrasive compact so-formed was machined to a diameter of about16 mm and a length of about 13 mm for wear and thermal stabilitytesting. Microstructural analysis was performed using a scanningelectron microscope and various photomicrographs are shown in FIGS.21A-21D. FIG. 21A shows a low magnification image of the superabrasivecompact illustrating the overall structure of the superabrasive compact.The superabrasive compact includes a superabrasive table 300 bonded tothe substrate 302. The superabrasive table 300 includes at least tworegions: an upper region 304 comprising diamond-silicon carbidecomposite and a lower region 306 bonded to the substrate that includescobalt swept-in from the substrate. FIG. 21B shows the microstructure ofthe upper region 304 of the superabrasive table 300. The upper region304 includes diamond grains (dark angular features) bonded together by amatrix (lighter region). The matrix is currently believed by theinventors to be silicon carbide and some un-reacted silicon. FIG. 21Cshows the microstructure of the lower region 306 of the superabrasivetable 300. The lower region 306 includes diamond grains (dark angularfeatures) bonded together by a matrix (lighter region). The matrix ofthe lower region 306 is currently believed by the inventors to includecobalt swept-in from the substrate, silicon carbide, and various cobaltsilicides (e.g., Co₂Si, CoSi, and CoSi₂). Carbon precipitates may alsobe present in the matrix of the lower region 306. FIG. 21D shows themicrostructure proximate the interface between the upper region 304 andthe lower region 306, which clearly shows the transition from the lowerregion 306 to the upper region 304 of the superabrasive table 300. Theinfiltration of cobalt into the upper region 304 is currently believedby the inventors to be prevented due to the formation of silicon carbidein the matrix of the upper region 304. In both the upper region 304 andthe lower region 306, the photomicrographs of FIGS. 21B-21D show a lackof bonding between the diamond grains. The lower region 306 of thesuperabrasive table 300 even showed a lack of bonding between diamondgrains despite the presence of cobalt, which is a metal-solventcatalyst.

Elemental analysis was performed on the superabrasive compact usingenergy-dispersive spectroscopy (“EDS”). FIG. 22 shows the concentrationof cobalt and silicon in weight percentage present in the superabrasivetable 300. As shown in FIG. 22, the concentration of cobalt drops toapproximately zero at or near the interface between the upper region 304and the lower region 306 of the superabrasive table 300. Silicon ispresent in both the upper region 304 and the lower region 306 of thesuperabrasive table 300.

The wear resistance of the superabrasive compact of example 5 was alsoevaluated by measuring the volume of the cutting element removed versusthe volume of Sierra White Granite rock removed in a vertical turretlathe at a 0.010 inch depth of cut and 100 RPM, with water used as acoolant. As shown in FIG. 23, the superabrasive compact of example 5exhibited wear resistance similar to the conventional, fine grain, PDCdescribed above in example 1. The thermal stability of the superabrasivecompact of example 5 was also evaluated by measuring the distance cut ina Sierra White Granite workpiece in a vertical turret lathe at a 0.110inch depth of cut and 100 RPM, without using coolant. The superabrasivecompact of example 5 was able to cut a distance approximately 13 timesgreater than that of a conventional, fine grain, PDC similar to theconventional PDC described above in example 1. Thus, the superabrasivecompact of example 5 exhibited a significantly greater thermal stabilitythan the conventional, fine grain, PDC.

Example 6

A mixture comprising about 90 weight percent diamond particles with aparticle size of about 15 μm to about 25 μm, about 5 weight percentdiamond particles with an average particle size of about 1 μm to about 3μm, and about 5 weight percent crystalline silicon particles with anaverage particle size of about 35 μm was loaded into a tungsten carbidelined milling jar and purged with argon gas. The mixture was then mixedin a Spex 8000D mixing/milling apparatus using tungsten carbide ballsfor about 1.67 hours.

A layer comprising about 2 grams of the milled mixture was distributedin the bottom of a niobium capsule. A cobalt-cemented tungsten carbidesubstrate was placed over the layer of the milled mixture, with a planarinterfacial surface of the substrate positioned adjacent to the layer.The niobium capsule, including the layer of the milled mixture andsubstrate, was cleaned using a high-temperature vacuum process andvacuum sealed. Then, the niobium capsule, including the layer of themilled mixture and substrate, was placed in the reaction zone of aconventional high-temperature, high-pressure apparatus and subjected toa temperature of about 1400° Celsius and a pressure of about 60 kilobarfor about 6 minutes.

The superabrasive compact so-formed was machined to a diameter of about16 mm and a length of about 13 mm. Microstructural analysis wasperformed using scanning electron microscope and variousphotomicrographs are shown in FIGS. 24A-24D. FIG. 24A shows a lowmagnification image of the superabrasive compact illustrating theoverall structure of the superabrasive compact. The superabrasivecompact includes a superabrasive table 400 bonded to the substrate 402.The superabrasive table 400 includes at least three regions: an upperregion 404 comprising diamond-silicon carbide composite, a lower region406 bonded to the substrate that includes cobalt swept-in from thesubstrate, a transition region 305 therebetween. FIG. 24B shows themicrostructure of the upper region 404 of the superabrasive table 400.The upper region 404 includes diamond grains (dark angular features)bonded together by a matrix (lighter region). The matrix is currentlybelieved by the inventors to be silicon carbide and some un-reactedsilicon. FIG. 24C shows the microstructure of the lower region 406 ofthe superabrasive table 400. The lower region 406 includes diamondgrains (dark angular features) bonded together by a matrix (lighterregion). The matrix of the lower region 406 is currently believed by theinventors to include cobalt swept-in from the substrate, siliconcarbide, and various cobalt silicides (e.g., Co₂Si, CoSi, and CoSi₂).Carbon precipitates may also be present in the matrix of the lowerregion 406. FIG. 24D shows the microstructure of the transition region405 and the upper region 404 of the superabrasive table 400. Theinfiltration of cobalt into the upper region 404 is currently believedto be prevented due to the formation of silicon carbide in the matrix ofthe upper region 404. In both the upper region 404 and the lower region406, the photomicrographs of FIGS. 24B-24D show a lack of bondingbetween the diamond grains. The lower region 406 of the superabrasivetable 400 even showed a lack of bonding between diamond grains despitethe presence of cobalt, which is a metal-solvent catalyst.

Elemental analysis was performed on the superabrasive compact using EDS.FIG. 25 shows the concentration in weight percentage of cobalt andsilicon present in the superabrasive table 400. As shown in FIG. 25, theconcentration of cobalt decreases more gradually with distance from thelower region 406 than in the superabrasive compact of example 5. Theconcentration of cobalt decreases across the transition region 405 to aconcentration of approximately zero at or near the interface between theupper region 404 and the transition region 405. Silicon is present inthe upper region 404, lower region 406, and transition region 405 of thesuperabrasive table 400.

Example 7

A mixture comprising about 86 weight percent diamond particles with amean particle size of about 10 μm and about 14 weight percentcrystalline silicon particles with an average particle size of about 35μm was loaded into a tungsten carbide milling jar and purged with argongas. The mixture was then mixed in a Spex 8000D mixing/milling apparatususing tungsten carbide balls for about 1.67 hours.

A first layer comprising about 2 grams of the milled mixture wasdistributed in the bottom of a niobium capsule. A tantalum foil barrierwas place adjacent to the milled mixture. A cobalt-cemented tungstencarbide substrate was then placed adjacent to the tantalum barrier. Theniobium capsule including the milled mixture, the tantalum barrier, andsubstrate was cleaned using a high-temperature vacuum process and vacuumsealed. Then, the niobium capsule, including the milled mixture,tantalum barrier, and substrate, was placed in the reaction zone of aconventional high-temperature, high-pressure apparatus and subjected toa temperature of about 1400° Celsius and a pressure of about 60 kilobarfor about 6 minutes to bond the various layers together and to thesubstrate. The superabrasive compact so-formed included a table ofdiamond-silicon carbide composite defining a cutting region, acobalt-cemented tungsten carbide substrate, and an intermediate tantalumbarrier that is bonded to the substrate and the table of diamond-siliconcarbide composite.

The superabrasive compact so-formed was machined to a diameter of about16 mm and a length of about 13 mm for wear and thermal stabilitytesting. The wear resistance of the superabrasive compact of example 7was also evaluated by measuring the volume of the cutting elementremoved versus the volume of Sierra White Granite rock removed in avertical turret lathe at a 0.010 inch depth of cut and 100 RPM, withwater used as a coolant. As shown in FIG. 26, the superabrasive compactof example 7 exhibited wear resistance similar to the conventional, finegrain, PDC described above in example 1. The thermal stability of thesuperabrasive compact of example 7 was also evaluated by measuring thedistance cut in a Sierra White Granite workpiece in a vertical turretlathe at a 0.110 inch depth of cut and 100 RPM, without using coolant.The superabrasive compact of example 7 was able to cut a distanceapproximately 5 times greater than that of a conventional, fine grain,PDC similar to the conventional PDC described above in example 1. Thus,the superabrasive compact of example 7 exhibited a significantly greaterthermal stability than the conventional, fine grain, PDC.

Example 8

A mixture comprising about 82 weight percent diamond particles with aparticle size of about 8 μm to about 16 μm, about 4 weight percentdiamond particles with an average particle size of about 1 μm to about 3μm, and about 14 weight percent crystalline silicon particles with anaverage particle size of about 35 μm was loaded into a tungsten carbidemilling jar and purged with argon gas. The mixture was then mixed in aSpex 8000D mixing/milling apparatus using tungsten carbide balls forabout 1.67 hours.

A first layer comprising about 1 gram of the milled mixture wasdistributed in the bottom of a niobium capsule. A tantalum foil barrierwas placed adjacent to the milled mixture. A second layer comprisingabout 1 gram of diamond particles with a particle size of about 15 μm toabout 25 μm was layered over the tantalum barrier. A cobalt-cementedtungsten carbide substrate was placed over the second layer of diamondparticles. The niobium capsule including the first layer, tantalumbarrier, second layer, and substrate was cleaned using ahigh-temperature vacuum process and vacuum sealed. Then, the niobiumcapsule, including the first layer, tantalum barrier, second layer, andsubstrate, was placed in the reaction zone of a conventionalhigh-temperature, high-pressure apparatus and subjected to a temperatureof about 1400° Celsius and a pressure of about 60 kilobar for about 6minutes to bond the various layers together and bond the second layer tothe substrate. The superabrasive compact so-formed included a table ofdiamond-silicon carbide composite defining a cutting region, acobalt-cemented tungsten carbide substrate, a polycrystalline diamondtable sintered with cobalt swept in from the substrate that is bonded tothe substrate and an intermediate tantalum barrier, with theintermediate tantalum barrier being bonded to the diamond-siliconcarbide composite and the polycrystalline diamond table.

The superabrasive compact so-formed was machined to a diameter of about16 mm and a length of about 13 mm for wear and thermal stabilitytesting. The wear resistance of the superabrasive compact of example 8was also evaluated by measuring the volume of the cutting elementremoved versus the volume of Sierra White Granite rock removed in avertical turret lathe at a 0.010 inch depth of cut and 100 RPM, withwater used as a coolant. As shown in FIG. 27, the superabrasive compactof example 8 exhibited wear resistance similar to the conventional, finegrain, PDC described above in example 1. The thermal stability of thesuperabrasive compact of example 8 was also evaluated by measuring thedistance cut in a Sierra White Granite workpiece in a vertical turretlathe at a 0.110 inch depth of cut and 100 RPM, without using coolant.The superabrasive compact of example 8 was able to cut a distanceapproximately 6 times greater than that of a conventional, fine grain,PDC similar to the conventional PDC described above in example 1. Thus,the superabrasive compact of example 8 exhibited a significantly greaterthermal stability than the conventional, fine grain, PDC.

Although the present invention has been disclosed and described by wayof some embodiments, it is apparent to those skilled in the art thatseveral modifications to the described embodiments, as well as otherembodiments of the present invention are possible without departing fromthe spirit and scope of the present invention. Additionally, the words“including” and “having,” as used herein, including the claims, shallhave the same meaning as the word “comprising.”

1. A rotary drill bit, comprising: a bit body configured to engage asubterranean formation, the bit body including a plurality of blades;and a plurality of superabrasive cutting elements, each of the pluralityof superabrasive cutting elements attached to a corresponding one of theplurality of blades, at least one of the plurality of superabrasivecutting elements including: a substrate; a superabrasive table, thesuperabrasive table comprising diamond-silicon carbide compositeincluding: a matrix including nanometer-sized silicon carbide grains;and micrometer-sized diamond grains dispersed through the matrix; and atleast one polycrystalline diamond layer disposed between the substrateand the superabrasive table, the at least one polycrystalline diamondlayer including a plurality of bonded-together diamond grains thatexhibit diamond-to-diamond bonding therebetween and define a pluralityof interstitial regions, at least a portion of the interstitial regionsincluding a metal-solvent catalyst disposed therein.
 2. The rotary drillbit of claim 1 wherein: the micrometer-sized diamond grains exhibit anaverage grain size of at least about 1 μm; and the nanometer-sizedsilicon carbide grains exhibit an average grain size of about 10 nm toabout 500 nm.
 3. The rotary drill bit of claim 2 wherein the matrixcomprises nanometer-sized diamond grains dispersed through the matrix,the nanometer-sized diamond grains exhibiting an average grain size ofabout 10 nm to about 500 nm.
 4. The rotary drill bit of claim 3 whereinthe nanometer-sized silicon carbide grains and the nanometer-sizeddiamond grains exhibit an average grain size of about 50 nm to about 200nm.
 5. The rotary drill bit of claim 2 wherein the nanometer-sizedsilicon carbide grains exhibit an average grain size of about 50 nm toabout 200 nm.
 6. The rotary drill bit of claim 1, further comprising: abarrier layer disposed between the at least one polycrystalline diamondlayer and the superabrasive table.
 7. The rotary drill bit of claim 6wherein an interface between the barrier layer and the substrateexhibits a selected non-planar topography.
 8. The rotary drill bit ofclaim 6 wherein the barrier layer comprises at least one of a refractorymetal or a carbide material.
 9. The rotary drill bit of claim 6 whereinthe barrier layer comprises tantalum, tungsten, niobium, molybdenum,titanium, or alloys thereof.
 10. The rotary drill bit of claim 1 whereinthe matrix comprises a toughening constituent dispersed therethrough.11. The rotary drill bit of claim 10 wherein the toughening constituentcomprises ceramic particles.
 12. The rotary drill bit of claim 11wherein the ceramic particles comprises silicon nitride particles,aluminum oxide particles, boron oxide particles, iron oxide particles,yttrium oxide particles, zinc oxide particles, zirconium oxideparticles, or combinations thereof.
 13. The rotary drill bit of claim 10wherein the toughening constituent comprises elongated alpha siliconcarbide grains at least partially surrounded by the nanometer-sizedsilicon carbide grains.
 14. The rotary drill bit of claim 1 wherein thesubstrate comprises a cemented carbide material.
 15. A rotary drill bit,comprising: a bit body configured to engage a subterranean formation,the bit body including a plurality of blades; and a plurality ofsuperabrasive cutting elements, each of the plurality of superabrasivecutting elements attached to a corresponding one of the plurality ofblades, at least one of the plurality of superabrasive cutting elementsincluding: a substrate; and a superabrasive table bonded to thesubstrate, the superabrasive table comprising diamond-silicon carbidecomposite including: a matrix including nanometer-sized beta siliconcarbide grains and alpha silicon carbide grains, the alpha siliconcarbide grains being present in an amount of about 1 weight percent toabout 20 weight percent of the superabrasive table; and micrometer-sizeddiamond grains dispersed through the matrix.
 16. A rotary drill bit,comprising: a bit body configured to engage a subterranean formation,the bit body including a plurality of blades; and a plurality ofsuperabrasive cutting elements, each of the plurality of superabrasivecutting elements attached to a corresponding one of the plurality ofblades, at least one of the plurality of superabrasive cutting elementsincluding: a substrate; and a superabrasive table comprisingdiamond-silicon carbide composite including: a matrix includingnanometer-sized silicon carbide grains; and micrometer-sized diamondgrains dispersed through the matrix; and at least one transition layerdisposed between the substrate and the superabrasive table, the at leastone transition layer comprising carbide particles and diamond grains,the at least one transition layer exhibiting a coefficient of thermalexpansion that is less than a coefficient of thermal expansion of thesubstrate and greater than a coefficient of thermal expansion of thesuperabrasive table.
 17. The rotary drill bit of claim 16 wherein thecarbide particles and the diamond grains of the at least one transitionlayer are cemented together with a binder.
 18. The rotary drill bit ofclaim 17 wherein: the carbide particles comprise tungsten-carbideparticles; and the binder comprises cobalt.
 19. The rotary drill bit ofclaim 16 wherein the at least one transition layer comprises: a firsttransition layer positioned adjacent to the substrate; and a secondtransition layer positioned adjacent to the superabrasive table, thefirst transition layer exhibiting a higher concentration of the carbideparticles than that of the second transition layer.
 20. A rotary drillbit, comprising: a bit body configured to engage a subterraneanformation, the bit body including a plurality of blades; and a pluralityof superabrasive cutting elements, each of the plurality ofsuperabrasive cutting elements attached to a corresponding one of theplurality of blades, at least one of the plurality of superabrasivecutting elements including: a substrate; and a superabrasive tablebonded to the substrate, the superabrasive table comprisingdiamond-silicon carbide composite including: a matrix includingnanometer-sized silicon carbide grains; and micrometer-sized diamondgrains dispersed through the matrix.